Hungry Galaxy Caught Feeding on Gas to Birth New Stars

Galaxies grow by pulling in material from their surroundings, gobbling down gas and dust. Before now, though, astronomers haven't been able to directly observe this phenomenon. Yet with ESO's Very Large Telescope, researchers have been able to study the very rare alignment between a distant galaxy and an even more distant quasar. This allowed the scientists to witness the galaxy in the act of feeding.

When galaxies grow and birth new stars, they quickly deplete their reservoirs of gas. This raw material must somehow be continuously replenished, or else the galaxy will stagnate. In the past, astronomers suspected that a galaxy collected cool gas from its surroundings through the use of its gravitational pull. The galaxy drags gas inward, which then circles around the galaxy, rotating with it before falling in. While some evidence of such accretion has been seen before, though, the motion of the gas and its other properties haven't been fully explored until now.

In order to receive a better glimpse at this "eating" behavior, researchers used two instruments known as SINFONI and UVES, both of which are mounted on ESO's VLT. The scientists were able to see how the galaxy itself was rotating and even could view the composition and motion of the gas outside of the galaxy. The actual ability to see these details was made possible in part by the rare alignment between the distant galaxy and a quasar, which is an extremely bright center of a galaxy powered by a supermassive black hole. The light from the quasar passed through the material around the foreground galaxy before reaching Earth, giving the scientists the light they needed to explore the details of the galaxy.

"The properties of this vast volume of surrounding gas were exactly what we would expect to find if the cold gas was being pulled in by the galaxy," said Michael Murphy, the co-author of the new study, in a news release. "The gas is moving as expected, there is about the expected amount and it also has the right composition to fit the models perfectly. It's like feeding time for lions at the zoo-this particular galaxy has a voracious appetite, and we've discovered how it feeds itself to grow so quickly."

The findings confirm that galaxies do gobble down surrounding material in order to expand. In addition, the researchers found out the composition of the fresh fuel that helps birth a future generation of stars.

The findings are published in the journal Science.